The degradation of imazapyr, fiumetsulam and thifensulfuron applied at 500, 40 and . M) g active ingredient (a.i,) ha"', respectively, to si!t loam soil was sttidied under laboratory and field conditions. Herbicide residues were analysed by a lentil {Lem culinaris L.) bioassay. Results showed ihat temperature had a significant effect on herbicide degradation. Vk'hereas the impact of soil organic matter ami pH were less well defined. Half-lives for iniazapyr, flumetsulam and thifensulfuron in soil samples from the 0-5 cm layer (64% organic carbon) at 15 "C were 125, 88 and 5-4 days, respectively, and 69, 30 and .^-9 days at 30 °C. ]n soil sampled from the 15-20 cm layer (3-5% organic carbon) half-lives were 155, 70 and 6-4 days, respectively, at 15 "C and 77, 24 and 4-8 days at 30 °C. A field experiment investigated the degradation and teaching of each herbicide under two precipitation regimes (natural precipitation (208 mm), and nattjral precipitation pJus 75 mm irrigation (283 mm)] over 4 months to a soil depth of 25 cm. Thifensiitfuron degraded rapidiy, whereas residues of flumetsulam and imazapyr leached below 25 cm in both the low-and highprecipitasion treatments after 4 months. Significant itnai^apyr residues were still present in the soil to 25 cm depth after 3 months. A miilt:component model for herbicide dissipation was developed and evaluated using data from the laboratory and fieid experiments. lntrottuction

A survey of weeds and weed management practices was conducted during 1997/98 in apple orchards and vineyards of Canterbury and Nelson/Marlborough regions of New Zealand. According to growers, mallow (Malva spp.) ranked as the most widespread weed in apple orchards of both regions. In vineyards, mallow was the most common weed in Nelson/Marlborough and the second most common weed in Canterbury. Other dominant weeds in Nelson/Marlborough included grasses, black nightshade (Solarium nigrum), fathen (Chenopodium album), and redroot (Amaranthus retroflexus). In Canterbury, grasses, clovers, fathen, and thistles were common. In almost all orchards knockdown herbicides were used but the use of residual herbicides varied. The total number of herbicide applications/year has increased in both regions over the past 10 years, but the proportional use of residual herbicides has declined. Some other weed management practices are used in orchards but a sound integration of these is commonly lacking.

Summary Three possible sources of field contamination by weed seeds were studied during 1983–86 in two areas of Fars Province, Iran. These sources were crop seed, irrigation water and sheep manure. Manure was found to be the most important, adding almost 10 million seeds ha−1 at each application. Farmer‐saved seed of wheat, the main crop of the area, added an average of 182,000 weed seeds ha−1. Irrigation water added no more than 120 seeds ha−1, but was able to carry seeds over long distances without affecting viability.

Field trials were undertaken over three years to determine the effect of tine weeding in organic pea (Pisum sativum) crops in Canterbury The tine weeding treatments were performed either as single or repeated passes at different times of crop growth Significant weed control and yield increase were achieved with a single pass of tine weeding either at preemergence or at the 2leaf stage of the crop On some occasions two passes of tine were required to control new weeds Late postemergence tine weeding did not have a positive effect on pea yield